Electrostatic discharge devices with high temperature arc resistance

ABSTRACT

High voltage static discharge device utilizes an insulative body portion of conventional plastic material for supporting conductive discharge points and ceramic stand-offs resistant to high temperature deterioration from arcing to space the body portion from an adjacent ground. Conductive elements which are connected to the same high voltage as the points are incorporated between and isolate the body portion from the ceramic stand-offs so that all portions of the body portion are at substantially the same voltage whereas the high voltage is imposed across the stand-offs.

United States Patent Barnett et al.

[ May 22, 1973 ELECTROSTATIC DISCHARGE DEVICES WITH HIGH TEMPERATURE ARC RESISTANCE Inventors: Guy F. Barnett, Warminster; Warren W. Levy, Cynwyd; Dolph Simons, Philadelphia, all of Pa.

Assignee: The Simco Company, Inc., Lansdale,

Filed: Aug. 17, 1971 Appl. No.: 172,499

US. Cl. ..317/2 F, 317/4 Int. Cl ..H05f 3/00, l-l0lt 19/04 Field of Search ..3 l7/2 F, 4, 262 R,

[56] References Cited UNITED STATES PATENTS 3,535,588 10/1970 Crook ..3l7/4 Primary Examiner-4.. T. Hix Attorney-Stanley Bilker' [5 7] ABSTRACT High voltage static discharge device utilizes an insulative body portion of conventional plastic material for supporting conductive discharge points and ceramic stand-offs resistant to high temperature deterioration from arcing to space the body portion from an adjacent ground. Conductive elements which are connected to the same high voltage as the points are incorporated between and isolate the body portion from the ceramic stand-offs so that all portions of the body portion are at substantially the same voltage whereas the high voltage is imposed across the stand-offs.

8 Claims, 6 Drawing Figures Patented May 22, 1973 3,735,198

2 Sheets-Sheet 1 INVENTORS auy r. 8A mvsrr WARREN w. LEVY DOLPH S/MONS JgM TORNEY 2 Sheets-Sheet 2 INVENTORS GUY f. BARNETT WARREN LEVY DOLPH SIMONS y? ATTORNEY Patented May 22, 1973 ELECTROSTATIC DISCHARGE DEVICES WITH HIGH TEMPERATURE ARC RESISTANCE This invention relates to high voltage ion producing devices, such as static charging bars or static neutralizers, in which a high voltage is applied to conductive discharge members or points in order to effect gas ionization and produce charged ions. More particularly, this invention relates to a system for protecting those plastic components that are used to insulate the high voltage carrying members from high temperature deterioration produced by arcing. That is, the present invention concerns a means for preventing burning, carbon tracking and evaporation or sublimation of high voltage insulators and supports when oil, dirt or other foreign matter collects on the surface thereof.

Static charging devices and static eliminators are utilized in the control of a great many processes in which it is desired to electrostatically regulate adhesion of one article to another, for example, the pinning of a sheet of paper to a preferred roll in a printing press or the neutralization of such sheets during stacking. In general, a high voltage is applied to discharge members, usually points, of such devices, DC. in the case of charging bars, and AC. in the case of neutralizers, so as to produce ions of one polarity or the other, or both polarities simultaneously. For example, in a charging bar, a D.C. potential of perhaps 25,000 volts positive or negative is applied to the points from a power source or supply unit having a current producing capability of up to milliamperes. As a result, if ground were to be juxtaposed to the discharge points, a substantial and heavy arcing could be produced. Since the industrial or commercial environments in which these high voltage ion producing devices are utilized are usually of marginal cleanliness at best, there is a tendency for oil, dirt, dust and other foreign conductive matter to deposit upon the surface of the insulating housing in which the points are embedded, upon the supports on which the bars are mounted to the machines, and upon the insulation of the leads and wires connecting the points to the high voltage power supply. Accordingly, a conductive path may be established from the high voltage points across the dirt or oil film to ground at the machine frame or casing for the power supply. As an outcome of the high temperature arcing produced, the plastic housing of the bar and/or wire insulation is subjected to carbon tracking, actual burning and evaporation or sublimation.

In order to prevent such high temperature deterioration of plastic components, it is possible to utilize special insulation and dielectric materials, such as ceramics, which are inherently high temperature resistant and not subject to the temperature effects caused by arcing. However, not only are such exotic ceramic materials --alumina, steatite, quartz, etc. extremely expensive, but also they lead to difficulty during assembly of the bar because of their hard and usually brittle characteristics. Thus, the use of a ceramic insulator member in excess of a few inches could be prohibitive in cost, whereas static charging bars of 80 inches or more in length are not uncommon. In contradistinction, plastic housings made of polyvinyl chloride or tetrafluoroethylene which are subject to high temperature arc deterioration can easily be extruded to any length and cut to size, and these plastics are a fraction of the cost of ceramics.

The present invention contemplates the adjacent of easily extruded and less expensive plastic housing portions polyvinyl chloride, tetrafluoroethylene, etc. as before, but relies on short sections of ceramic components to act as end caps or stand-offs where the bars are mounted to grounded machine frames or connected to grounded members. A conductive element is disposed and incorporated between the heat sensitive plastic members and its next adjacent heat resistant ceramic component so as to isolate the two materials from each other. The very same high voltage which is applied to the discharge points or other ionizing means is applied to the conductive isolating members so that high potential is not actually imposed across the sensitive plastic; the entire high voltage gradient is thereby applied across the ceramic members between the conductive isolating members and ground. Thus, any arcing, if such does occur, is developed across the ceramic which is not damaged, and any oil or dirt film which builds up on the ceramicsurface is easily cleaned off by virtue of the smooth, hard exterior finish of ceramic. Since all portions of the plastic components will be at the same potential, no arcing can be created by conductive film build up on the plastic surface.

It is therefore an object of this invention to provide a high voltage static discharge device which is not subject to high temperature deterioration resulting from arcing.

Another object of this invention is to provide a high voltage static discharge device which is easily and economically produced and which is capable of being maintained in a condition that is resistant to arcing.

Other objects of this invention are to provide an improved device of the character described which is sturdy in construction and both highly efficient and effective in operation.

With the above and related objects in view, this invention consists of the details of construction and combination of parts as will be more fully understood from the following detailed description when read in conjunction with the accompanying drawing in which:

FIG. 1 is a perspective view of a high voltage static charging bar embodying this invention.

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1.

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2.

FIG. 4 is a sectional view taken along lines 44 of FIG. 2.

FIG. 5 is a perspective view of another embodiment of the present invention.

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 5.

Referring now in greater detail to the drawings in which similar reference characters refer to similar parts, there is shown a static charging bar embodying this invention comprising a body portion or casing, generally designated as A, a plurality of conductive discharge points B projecting from the casing and coupled to a high voltage power supply G by way of a cable C, and stand-offs or posts D for mounting the bar upon the frame of a machine or apparatus. In one embodiment of this invention, as shown in FIGSJl and 2, terminal insulators E (end caps) are incorporated at each end of the body portion A and straps or brackets F are used to mount the bar upon the machine frame, in this first embodiment the stand-offs D being utilized to support the center portion of the bar. The .end cap insulator portions E and the stand-offs D (or the posts D of FIGS. 5 and 6) are made of special material which is resistant to high temperature arcing conditions. The casing or body portion A of the bar is fabricated of conventional plastic materials. Conductive annular disks E1 which are connected to the same high voltage as the points are incorporated between and isolate the casing A from the terminal insulative portions E. Similarly, conductive rings D] on the posts and stand-offs D are connected to the high voltage and isolate the casing A from the special insulative portion of the latter members D. In this manner, the entire burden of insulating the bar from ground (i.e.-the machine frame) is borne by the high temperature resistant end cap insulators E and/or the high temperature resistant insulative portion 30 of the posts D. On the other hand, no voltage gradient exists across the sensitive plastic portion of the casing A since the same high voltage exists at the points B and at each zone E1 or D1 where the bar is insulatively supported adjacent a grounded reference.

The casing A includes an elongated insulative portion 12 which is extruded from a suitable plastic material, such as tetrafluoroethylene. Upwardly extending flanges 14 define a longitudinally disposed central channel 16 through which the points B project, and slots which receive the corresponding edges of split tubular member 18. The split tubular housing 18 is extruded from an inexpensive plastic insulating material, such as polyvinyl chloride, and is cut to a length generally coextensive with the length of the channel portion 12. This length may range from a few inches to over 80 inches.

The cable C is a conventional insulated wire which includes a conductive core 20 and a plurality of insulative layers or sheaths to insure a high dielectric breakdown rating. The cable C is snugly passed through a bore in the channel portion 12 until it is substantially in registration with the opposite end. The points B which are double ended needles of steel for example, are pressed through longitudinally spaced holes transversely extending through the channel portion 12 until the points pierce the cable insulation and engage the conductive inner core thereof.

The terminal insulators or end caps E are molded of high temperature resistant dielectric material, such as ceramic, alumina, steatite, quartz or the like. The outboard portion 22 of each end cap E has a periphery which generally corresponds to that of the tubular housing 18 and includes a tongue portion 24 which is inserted into and interfits snugly within the cavity defined between the channel strip 12 and housing 18 walls. A bead 25 adjacent the end of each ceramic insulator E provides a convenient stop for supporting the mounting straps F. The straps or brackets F are entirely conventional, made of a metal such as steel, and serve as a means for securing the bar upon the frame Fl of a machine.

The annular disks El are interposed between the outboard portion 22 of the end caps E and the body portion A. Each disk E1 is fabricated of conductive material, such as brass or steel, and includes a tab portion 26 having an aperture securely embracing the last discharge point B in the line so as to make good electrical connection and contact therewith. Of course, other modes of connection of the disks E1 to the high voltage are contemplated without departing from the spirit of the invention.

The center stand-offs D of the FIG. 1 embodiment and the end posts D of the FIG. 5 embodiment are basically identical. Each includes a leg portion 30 of high temperature resistant insulative material, ceramic or the like, which supportively spaces the static bar from the machine frame F], and a conductive ring portion D1, which is connected to the high voltage by way of a gull-wing shaped clamp D2. The clamp D2 is made of steel for example and includes a central portion 32 which interfits within the channel 16 of strip 12. A hole in the central portion 32 snugly embraces a centrally located point B such that a secure electrical contact is formed between the point B, the clamp D2 and the ring D1. An insulative collar 36 encircles the split tubular portion 18 under the ring D1 in order to lend support and to permit uniform distribution of pressure. The ring D1 itself may be secured to the ceramic leg portion 30 by means of a threaded screw or bolt 38.

The cable C passes through a longitudinal bore 40 in the end cap E and is held in position therein by a threaded plastic fitting 42. The central conductor 20 of the cable C is then connected to the high voltage DC. power supply G which is capable of supplying up to 50,000 volts and up to 20 milliamperes current.

In the embodiment shown in FIGS. 5 and 6, caps 44 and 46 are utilized to plug the ends of the body portion A, and except for the use of the end post mounting, their construction is otherwise basically the same as FIG. 1 embodiment. However, since a film of dirt or oil may collect on the surface of cable C and the cap 46 between ring D1 and the grounded casing of the power supply G (or a metal machine frame which the cable C may contact), it is preferred that end cap 46 be of ceramic in order to facilitate cleaning and resist high temperature deterioration by burning, carbon tracking or evaporative sublimation.

As is apparent from the foregoing description, all portions of the heat sensitive insulative body portion A are effectively isolated by a conductive member from the ceramic post or other high temperature resistant material which couples the bar to an adjacent ground. Since the points and the isolating conductive members are all at the same high voltage, a film of oil or dirt collecting on the surface of the body portion A cannot cause arcing thereacross. In contradistinction, the entire voltage gradient would be developed across the resistant ceramic material which is easily cleaned, and even if dust, dirt or oil should cause an arc to develop across the ceramic posts D or insulating end caps E, no damage would result.

Although this invention is described in considerable detail, such description is intended as being illustrative rather than limiting, since the invention may be variously embodied without departing from the spirit, and the scope of the invention is to be determined as claimed.

What is claimed is: l. A high voltage electrostatic discharge device comprising:

an insulative casing subject to high temperature deterioration produced by arcing, discharge means for effecting high voltage gas ionization supported in said casing and outwardly projecting therefrom,

at least one insulative member having the characteristic of being resistive to high temperature arc deterioration spacing said insulated casing from an adjacent ground,

a conductive element interposed between said insulated casing and each of said next adjacent insulative members and isolating the surface of said insulated casing therefrom, and

means for applying a high voltage with respect to ground to said discharge means and simultaneously to each of said conductive elements, whereby said insulated casing is isolated at a uniform voltage and wherein the entire high voltage with respect to ground is imposed across said insulative members.

2. The electrostatic discharge device of claim 1 wherein the means for applying a high voltage with respect to ground constitutes a DC. power supply.

3. The electrostatic discharge device of claim 2 wherein said discharge means comprise a plurality of points.

4. The electrostatic discharge device of claim 3 wherein said insulated casing is of thermoplastic material and said insulative members are each ceramic.

5. The electrostatic discharge device of claim 4 wherein said insulated casing is of elongated configuration, and one insulative member is coupled to each end thereof.

6; The electrostatic discharge device of claim 5 wherein at least one of said insulative members comprises a post transversely disposed with respect to said insulated casing.

7. The electrostatic discharge device of claim 6 wherein each of the conductive elements comprises a ring attached to the next adjacent point.

8. The electrostatic discharge device of claim 5 wherein each of said insulative end members is longitudinally aligned with respect to said insulated casing 

1. A high voltage electrostatic discharge device comprising: an insulative casing subject to high temperature deterioration produced by arcing, discharge means for effecting high voltage gas ionization supported in said casing and outwardly projecting therefrom, at least one insulative member having the characteristic of being resistive to high temperature arc deterioration spacing said insulated casing from an adjacent ground, a conductive element interposed between said insulated casing and each of said next adjacent insulative members and isolating the surface of said insulated casing therefrom, and means for applying a high voltage with respect to ground to said discharge means and simultaneously to each of said conductive elements, whereby said insulated casing is isolated at a uniform voltage and wherein the entire high voltage with respect to ground is imposed across said insulative members.
 2. The electrostatic discharge device of claim 1 wherein the means for applying a high voltage with respect to ground constitutes a D.C. power supply.
 3. The electrostatic discharge device of claim 2 wherein said discharge means comprise a plurality of points.
 4. The electrostatic discharge device of claim 3 wherein said insulated casing is of thermoplastic material and said insulative members are each ceramic.
 5. The electrostatic discharge device of claim 4 wherein said insulated casing is of elongated configuration, and one insulative member is coupled to each end thereof.
 6. The electrostatic dIscharge device of claim 5 wherein at least one of said insulative members comprises a post transversely disposed with respect to said insulated casing.
 7. The electrostatic discharge device of claim 6 wherein each of the conductive elements comprises a ring attached to the next adjacent point.
 8. The electrostatic discharge device of claim 5 wherein each of said insulative end members is longitudinally aligned with respect to said insulated casing 